In the context of electricity, a surge is a sudden transient rise in the line voltage. These surges can damage the transmission line itself and the equipment connected to it. Surges typically occur as the result of a lightning strike, line fault, or switching. A surge arrestor serves to limit a surge voltage.A surge arrestor is connected across the equipment to be protected, just like the guard in front of a building. As long as the voltage is below a design limit (the clamp voltage), the arrestor acts as a high resistance across the line and draws almost no current. When the voltage tries to rise beyond the allowable level, the arrestor offers some resistance and diverts most of the surge to ground. If the surge energy is within the capability of the arrestor, the line voltage will be kept at the designed level. If the surge is stronger, the voltage may raise somewhat above this value. Surge arrestors for high power transmission lines are generally the metal-oxide varistor (MOV) type. Air gaps may be used alone or in conjunction with MOVs. For lower power levels and in electronics, semiconductors and passive components may be used. The surge arrestor may alternately be called a Surge Limiter or a Transient Voltage Suppressor (TVS). Read more Read less